Electronic energy levels and stereochemistry of the cis-distorted octahedral complex nitritobis-(2,2′-bipyridyl)copper(II) nitrate

The polarised single-crystal electronic and e.s.r. spectra of [Cu bipy2(ONO)]NO3(bipy = 2,2′-bipyridyl) have been determined and related to the cis-distorted octahedral molecular structure of this complex. The single-crystal e.s.r. spectra establish the short Cu–N bond as the z axis, and the x and y axes as bisecting the in-plane copper–ligand bonds. The polarised electronic spectra are interpreted in C2ν symmetry with the principle C2 axis lying along the x axis of the magnetic co-ordinates. Crystal-field calculations and the e.s.r. spectra establish a dz2 orbital as the ground state; the polarisation data then suggests the partial one-electron orbital energy sequence dz2 > dxy > dz2–y2 > dxz. The position of the dyz orbital is uncertain but is probably close to that of the dxz orbital. The g-value expressions for this environment are calculated.The stereochemistry of [Cu bipy2(ONO)]NO3 is compared with those of [Cu bipy2l]l and Cu dmp Cl2,H2O (dmp = 2,9-dimethyl-1,10-phenanthroline), and the description of the first complex as cis-distorted octahedral is justified. The relationship between regular cis-octahedral, trigonal bipyramidal and square-based pyramidal configurations is examined and a correlation diagram between the one-electron energy levels involved, is suggested.